1. Field of the Invention
This invention relates to a precision valve assembly which can be used for accurately controlling the flow of fluids delivered to a patient. More specifically, it relates to a precision valve assembly which is particularly suitable for use in conjunction with volumetric control monitors used with fluid administration sets to deliver exact amounts of parenteral and other fluids to patients at precise flow rates.
2. Description of the Prior Art
Medical patients in and out of the hospital frequently require continuous administration of parenteral and other fluids, and these must often be infused at precise, controlled flow rates. Traditionally, an attendant has adjusted a pinch clamp mounted on flexible, plastic tubing to provide a desired drop rate. The conformation of this flow passageway of the pinched tubing is not constant and gradually changes due to plastic creep and hoop tension. To compensate for these changes and avoid a variable flow rate, an attendant must periodically readjust the clamp setting to obtain the desired drop rate.
A variety of flow controllers have been devised which adjust the flow rate of parenteral fluids by automatically operating a pinch clamp or other valve assembly in response to drop rate changes as determined by photoelectric methods. Each drop falls through and interrupts a beam of light, the interruptions are counted, and the count is compared with a desired count. Such a counter is disclosed in U.S. Pat. No. 4,014,010, and systems responsive to such a counter are described in U.S. Pat. Nos. 4,204,538 and 4,207,871.
The flow systems and counters disclosed in the above patents require constant adjustment because of the limitations of the valve assembly, making necessary a large electric energy supply. Portable units are then unduly bulky because of the large battery size. The prior art units tend to be heavy, complex and require operating voltages which are undesirable in a hospital environment, further detracting from their usefulness, particularly as applied to ambulatory patients.
U.S. Pat. No. 3,396,939 discloses a valve structure incorporating a frustuconical member which seats on a valve seat in response to the rotation of portions of the valve assembly. U.S. Pat. No. 2,806,654 discloses a control valve including ball elements. The balls travel in radial tracks and activate a snap action mechanism which in turn drives a valve member to a closed position. These patents are directed to off-on valves used in high pressure systems.